STEP STRUCTURE DURING ORGANOMETALLIC VAPOR-PHASE EPITAXIAL-GROWTH OF ORDERED GAINP

The nature of the steps on the nominally (001)-oriented surface of Gao (0.5)In(0.5)P lattice matched to GaAs has been studied using high reso lution atomic force microscopy. The layers were grown by organometalli c vapor phase epitaxy (OMVPE) at a temperature of 620 degrees C on sub strates misoriented by angles, curly theta(m), from 0 to 9 degrees tow ard the [(1) over bar 10] direction in the lattice. An array of bunche d steps from 25 to 50 Angstrom in height, depending on the substrate m isorientation angle, is observed on the surface. An unusual feature of these bunched or super-steps, as compared to those seen for GaAs surf aces, is that they have relatively short lengths of a few thousand Ang stroms. In addition, not all of the steps congregate into the surface steps. Thus, the surface consists of three ''phases'': (001) flats, (1 1n) facets, and misoriented areas covered by an array of monolayer ste ps. The fraction of steps contained in the supersteps decreases monoto nically as curly theta(m) increases from 3 to 9 degrees. Again, this d iffers from reports of the nature of GaAs surfaces grown under similar conditions where essentially all of the steps congregate into superst eps. The value of n for the (11n) facets also varies with misorientati on angle: The angle between the (001) and the (11n) facets increases f rom approximately 11-12 degrees for curly theta(m) = 3 degrees to near ly 30 degrees for curly theta(m) = 9 degrees. An attempt was made to c orrelate the surface structure with ordering, which is observed to var y significantly with misorientation angle. The degree of order is foun d to increase monotonically with the fraction of steps forming superst eps.